DRY-COMPRESSION COMPRESSOR AND METHOD FOR OIL SEPARATION FOR A DRY-COMPRESSION COMPRESSOR

Abstract

The invention relates to a dry-compressing or oil-free compressor for generating a compressed gas and a method for oil separation for a dry-compressing compressor (1). The compressor has a compressor housing (4), a compression chamber (5) and at least one oil chamber (19a, 19b), in which an oil-lubricated bearing (18a, 18b) of the rotor bearing (16) is accommodated, as well as a shaft seal arrangement (10a, 10b), which is arranged between the oil-lubricated bearing (18a, 18b) and the compression chamber (5). The shaft seal arrangement (10a, 10b) has an outer seal (17a, 17b) facing the oil-lubricated bearing (18a, 18b) and an inner seal (12a, 12b) facing the compression chamber (5), wherein at least one sealing gas chamber (13a, 13b, 13c, 13d) for receiving sealing gas is formed between the outer seal (17a, 17b) and the inner seal (12a, 12b). The oil chamber (19a, 19b) has at least one gas inlet for a sealing gas flow from the sealing gas chamber (13a, 13b, 13c, 13d) and a gas outlet (26) for connection to an oil separator (30, 31, 32, 33). The oil chamber (19a, 19b) provides an oil chamber pressure p.sub.OR that exceeds the ambient pressure p.sub.0 of the compressor housing (4) by an oil separation pressure difference ?p.

Claims

1. Dry-compressing compressor (1) for generating a compressed gas, having one or more compressor stages (2, 3), comprising a compressor housing (4), at least one compressor rotor (6, 7, 8), which is rotatably mounted in relation to the compressor housing (4) via a rotor bearing (16), wherein the compressor housing (4) comprises a compression chamber (5) for compressing gas drawn in by the compressor rotor (6, 7, 8) and at least one oil chamber (19a, 19b), in which at least one oil-lubricated bearing (18a, 18b) of the rotor bearing (16) for mounting a shaft section (11a, 11b) of the compressor rotor (6, 7, 8) is accommodated, a shaft seal arrangement (10a, 10b) assigned to the shaft section (11a, 11b), which is arranged between the oil-lubricated bearing (18a, 18b) and the compression chamber (5) to seal the compression chamber (5) against oil ingress from the oil chamber (19a, 19b), wherein the shaft seal arrangement (10a, 10b) has an outer seal (17a, 17b) facing the oil-lubricated bearing (18a, 18b), in particular without contact, and an inner seal (12a, 12b) facing the compression chamber (5), wherein at least one sealing gas chamber (13a, 13b, 13c, 13d) for accommodating sealing gas is formed between the outer seal (17a, 17b) and the inner seal (12a, 12b), wherein the oil chamber (19a, 19b) has at least one gas inlet for a sealing gas flow from the sealing gas chamber (13a, 13b, 13c, 13d) and a gas outlet (26) for connection to an oil separator (30, 31, 32, 33), and wherein the oil chamber (19a, 19b) is designed to provide an oil chamber pressure p.sub.OR which exceeds the ambient pressure p.sub.0 of the compressor housing (4) by an oil separation pressure difference ?p, which is preferably at least 20 mbar.

2. Dry-compressing compressor (1) according to claim 1, characterized in that the gas outlet (26) of the oil chamber (19a, 19b) is connected to at least one oil separator (30, 31, 32, 33).

3. Dry-compressing compressor (1) for generating a compressed gas, having one or more compressor stages (2, 3), comprising a compressor housing (4), at least one compressor rotor (6, 7, 8), which is rotatably mounted in relation to the compressor housing (4) via a rotor bearing (16), wherein the compressor housing (4) comprises a compression chamber (5) for compressing gas drawn in by the compressor rotor (6, 7, 8) and at least one oil chamber (19a, 19b), in which at least one oil-lubricated bearing (18a, 18b) of the rotor bearing (16) for mounting a shaft section (11a, 11b) of the compressor rotor (6, 7, 8) is accommodated, a shaft seal arrangement (10a, 10b) assigned to the shaft section (11a, 11b), which is arranged between the oil-lubricated bearing (18a, 18b) and the compression chamber (5) to seal the compression chamber (5) against oil ingress from the oil chamber (19a, 19b), and has a seal (17a, 17b), wherein the oil chamber (19a, 19b) has at least one gas inlet for a leakage gas flow from the shaft seal arrangement (10a, 10b) and a gas outlet (26) which is connected to at least one oil separator (30, 31, 32, 33), wherein the oil chamber (19a, 19b) is designed to provide an oil chamber pressure p.sub.OR which exceeds the ambient pressure p.sub.0 of the compressor housing (4) by an oil separation pressure difference ?p, which is preferably at least 20 mbar.

4. Dry-compressing compressor (1) according to claim 3, characterized in that the seal (17a, 17b) is an outer seal (17a, 17b) facing the oil-lubricated bearing (18a, 18b), and the shaft seal arrangement (10a, 10b) also has an inner seal (12a, 12b) facing the compression chamber (5), wherein at least one sealing gas chamber (13a, 13b, 13c, 13d) for receiving sealing gas is formed between the outer seal (17a, 17b) and the inner seal (12a, 12b), wherein the leakage gas flow from the shaft seal arrangement (10a, 10b) is a sealing gas flow from the sealing gas chamber (13a, 13b, 13c, 13d).

5. Dry-compressing compressor (1) according to claim 3, characterized in that the gas inflow of the oil chamber (19a, 19b) is formed by at least one sealing gap (14a, 14b) of the seal (17a, 17b).

6. Dry-compressing compressor (1) according to claim 3, characterized in that the compressor (1) comprises at least one pressure sensor (25) for detecting the oil chamber pressure p.sub.OR.

7. Dry-compressing compressor (1) according to claim 3, characterized in that the oil separator (30, 31, 32, 33), comprises a plurality of separation stages.

8. Dry-compressing compressor (1) according to claim 3, characterized in that the sealing gas flow and/or the leakage gas flow is an air flow, wherein an air outlet (37) leads downstream of the oil separator (30, 31, 32, 33) into the free environment of the compressor (1).

9. Dry-compressing compressor (1) according to claim 3, characterized in that the compressor (1) comprises an oil return line (34) for oil separated in the oil separator (30, 31, 32) into the oil chamber (19a, 19b).

10. Dry-compressing compressor (1) according to claim 3, characterized in that the compressor (1) comprises a blow-off valve (47) for releasing the oil chamber pressure p.sub.OR from the oil chamber (19a, 19b).

11. Dry-compressing compressor (1) according to claim 3, characterized in that the rotor bearing (16) comprises an oil-lubricated suction-side bearing (18a) and an oil-lubricated pressure-side bearing (18b), each of which rotatably supports a shaft section (11a, 11b) of the compressor rotor (6, 7, 8) with respect to the compressor housing (4), wherein the compressor housing (4) has a suction-side oil chamber (19a), in which the suction-side bearing (18a) is accommodated, and a pressure-side oil chamber (19b), in which the pressure-side bearing (18b) is accommodated, wherein the suction-side oil chamber (18a) and the pressure-side oil chamber (18b) are connected to one another.

12. Dry-compressing compressor (1) according to claim 1, characterized in that the rotor bearing (16) comprises an oil-lubricated suction-side bearing (18a) and an oil-lubricated pressure-side bearing (18b), each of which rotatably supports a shaft section (11a, 11b) of the compressor rotor (6, 7, 8) with respect to the compressor housing (4), wherein a suction-side shaft seal arrangement (10a) is provided for the suction-side bearing (18a) and a pressure-side shaft seal arrangement (10b) is provided for the pressure-side bearing (18b), wherein the suction-side sealing gas chamber (13a, 13c) of the suction-side shaft seal arrangement (10a) and the pressure-side sealing gas chamber (13b, 13d) of the pressure-side shaft seal arrangement (10b) are connected to one another via a sealing gas connection line (42).

13. Dry-compressing compressor (1) according to claim 1, characterized in that the shaft seal arrangement (10a, 10b) additionally has a middle seal (15a, 15b), between the outer seal (17a, 17b) and the inner seal (12a, 12b), wherein an outer sealing gas chamber (13a, 13b) for receiving sealing gas is formed between the outer seal (17a, 17b) and the middle seal (15a, 15b) and an inner sealing gas chamber (13c, 13d) for receiving sealing gas is formed between the middle seal (15a, 15b) and the inner seal (12a, 12b).

14. Dry-compressing compressor (1) according to claim 1, characterized in that the compressor (1) has a sealing gas supply (50, 51, 51a, 51b) by means of which the sealing gas chamber pressure p.sub.SGR in at least one sealing gas chamber (13a, 13b, 13c, 13d) is variably adjustable.

15. Dry-compressing compressor (1) according to claim 1, characterized in that the compressor (1) has at least one sealing gas buffer volume (48, 55) between a sealing gas feed (58) and a sealing gas chamber (13a, 13b, 13c, 13d).

16. Dry-compressing compressor (1) according to claim 1, characterized in that the compressor (1) comprises at least one pressure sensor (45, 45a, 45b) for detecting a sealing gas chamber pressure p.sub.SGR.

17. Dry-compressing compressor (1) according to claim 1, characterized in that control unit (60) is provided, which is designed to monitor the sealing gas chamber pressure p.sub.SGR and/or the oil chamber pressure p.sub.OR and/or the differential pressure between the sealing gas chamber pressure p.sub.SGR and the oil chamber pressure p.sub.OR.

18. Dry-compressing compressor (1) according to claim 1, characterized in that a control unit (60) is designed to set the sealing gas chamber pressure p.sub.SGR in the sealing gas chamber (13a, 13b, 13c, 13d), such that the sealing gas chamber pressure p.sub.SGR is higher than the oil chamber pressure p.sub.OR in the oil chamber (19a, 19b).

19. Dry-compressing compressor (1) according to claim 1, characterized in that the compressor (1) has a sealing gas supply valve (51) designed as a pressure-reducing valve.

20-22. (canceled)

23. Method for oil separation for a dry-compressing compressor (1) having one or more compressor stages (2, 3) for generating a compressed gas according to claim 1, having an oil-lubricated rotor bearing (16) of at least one compressor rotor (6, 7, 8) of the compressor (1), wherein the method comprises the steps of: introducing a leakage gas flow, which flows out of a shaft seal arrangement (10a, 10b) assigned to a shaft section (11a, 11b) of the compressor rotor (6, 7, 8), into an oil chamber (19a, 19b) of a compressor housing (4) of the compressor (1), in which at least one oil-lubricated bearing (18a, 18b) of the rotor bearing (16) is accommodated, providing an oil chamber pressure p.sub.OR in the oil chamber (19a, 19b) which exceeds the ambient pressure p.sub.0 of the compressor housing (4) by an oil separation pressure difference ?p, feeding a gas flow from the oil chamber (19a, 19b) to an oil separator (30, 31, 32, 33).

24-27. (canceled)

Description

[0078] FIG. 1 shows a schematic representation of a first embodiment of a dry-compressing compressor according to the invention;

[0079] FIG. 2 shows a schematic representation of a second embodiment of a dry-compressing compressor according to the invention having shaft seal arrangements on the suction side and pressure side, each with two sealing gas chambers;

[0080] FIG. 3 shows a schematic representation of a third embodiment of a dry-compressing compressor according to the invention having an external sealing gas supply and a sealing gas buffer volume;

[0081] FIG. 4 shows a schematic representation of a fourth embodiment of a dry-compressing compressor according to the invention having two compressor stages;

[0082] FIG. 5 shows a schematic representation of a fifth embodiment of a dry-compressing compressor according to the invention having two compressor stages and several sealing gas pressures.

[0083] In the following description of the invention, the same reference symbols are used for identical and identically acting elements.

[0084] The embodiments of the invention described below with reference to FIGS. 1 to 5 each illustrate different aspects of the invention. The embodiments shown can be combined with each other, unless technically contradictory. In particular, individual described components or systems of the dry-compressing compressors according to the invention, such as pressure sensors, the design of the oil separator (multi-stage design, design of the separator stages), the oil return, sealing gas supply and sealing gas feed, negative pressure protection device and, in particular, the control unit and process control system can be supplemented in each embodiment, are interchangeable between the embodiments and can be combined with each other, unless technically contradictory. Unless otherwise indicated, the letter a following the reference signs refers to the suction side 85 and the letter b to the pressure side 86 of the compressor 1. For example, 19a refers to the suction-side oil chamber and 19b to the pressure-side oil chamber.

[0085] FIG. 1 shows a (single-stage) dry-compressing or oil-free compressing compressor 1 with oil-lubricated bearings 18a, 18b in a compressor housing 4. The compressor 1 draws in air as the gas to be compressed via the air inlet 70 on the suction side 85, compresses the air and conveys the compressed air from the pressure side 86 via the compressed air outlet 76 to the application not shown, typically into a compressed air network of a consumer.

[0086] The bearings 18a, 18b of the rotor bearing 16 are lubricated with oil and arranged in the oil chambers 19a, 19b of the compressor housing 4, in which the lubricating oil mixes with gas to form a gas-air mixture in the form of an oil mist containing aerosols from the lubricating oil. However, the compression chamber 5, in which the gas is compressed by rotating one or more compressor rotors 6, should remain free of oil. For this purpose, the shaft seal arrangements 10a, 10b are sealed against the oil chambers 19a, 19b with inner seals 12a, 12b and outer seals 17a, 17b. The seals 17a, 17b and 12a, 12b are non-contacting and not completely sealed due to high circumferential speeds and temperatures during operation. A narrow sealing gap 14a, 14b remains on the circumference of the shaft sections 11a, 11b of the compressor rotor 6, which are assigned to the shaft seal arrangements 10a, 10b, through which a gas flow can flow in the direction of the compression chamber 5, or vice versa, depending on the pressure gradient. This gas flow occurs due to the leakage of the seals 17a, 17b and 12a, 12b. However, no lubricant may enter the compression chamber 5 or the surroundings 9 of the compressor housing 4 in order not to jeopardize the purity of the compressed gas.

[0087] According to one embodiment of the invention, a sealing gas system counteracts the entry of lubricant into the compression chamber 5. A sealing gas chamber 13a, 13b is arranged between the inner seal 12a, 12b and the outer seal 17a, 17b. The sealing gas chambers 13a, 13b of suction-side and pressure-side shaft seal arrangements 10a and 10b are connected to each other via sealing gas connection lines 42, which can also be designed as bores in the compressor housing 4. Sealing gas flows from the sealing gas chambers 13a, 13b into the oil chambers 19a, 19b at a corresponding pressure drop. The oil chambers 19a, 19b are each sealed off from the environment 9 in such a way that they can build up and maintain an oil chamber pressure p.sub.OR that is higher than the ambient pressure p.sub.0, i.e. an overpressure.

[0088] There is usually an air leakage flow from the compression chamber 5 into the sealing gas chamber 13b via the inner seal 12b on the pressure side 86. At higher pressure in the compression chamber 5, the air leakage flow is higher. Therefore, the air leakage flows at the inner seals 12a and 12b are different. On the suction side 85, the leakage flow via the inner seal 12a is smaller than on the pressure side 12b and can reverse in the opposite direction. On the suction side 85, some sealing gas can also be drawn into the compressor chamber 5 via the inner seals 12a during load operation, as the pressure here is lower over a large part of the circumference of the compressor rotors 6 than in the sealing gas chamber 13a. In normal load operation, the sealing gas chamber pressure p.sub.SGR is maintained in the connected sealing gas chambers 13a, 13b due to the leaks in the inner seal 12a and especially the inner seal 12b.

[0089] In certain operating states, e.g. with low compression pressures or transient processes, sealing gas is additionally supplied to the sealing gas chambers 13a, 13b via a sealing gas supply line 50 and a regulated sealing gas supply valve 51. The sealing gas supply valve 51 can also be designed as a mechanical pressure reducing valve, especially for more cost-effective designs of the compressor 1, wherein a control unit 60 described below could also be dispensed with. In the embodiment shown in FIG. 1, the additional sealing gas (sealing air) is branched off from the compressed air flow fed to the compressed air outlet 76 and fed to the sealing gas supply ducts 41 as an internal sealing gas feed via the sealing gas supply valve 51. The sealing gas chamber pressure p.sub.SGR in the sealing gas chambers 13a, 13b is thus always set higher during operation than the oil chamber pressure p.sub.OR in the oil chambers 19a, 19b, which are connected to each other via the connection line 21. Due to the described pressure gradient from the sealing gas chambers 13a, 13b to the oil chamber 19a, 19b (p.sub.OR<p.sub.SGR), air leaks are generated (during operation) via the outer seals 17a, 17b from the dry sealing gas chambers 13a, 13b into the oil chambers 19a, 19b, which flow into the oil chambers 19a, 19b as sealing gas flows. Due to this pressure difference across all outer seals 17a and 17b, the lubricant, i.e. the oil, is held in the oil chambers 19a, 19b despite the sealing gap 14a, 14b and at the same time a sealing gas flow, which can contain supplied sealing air and leakage air from the compression chamber 5, is forced into the oil chambers 19a, 19b, where the oil chamber pressure p.sub.OR builds up or prevails. The sealing gas chamber pressure p.sub.SGR is detected by the pressure sensor 45. The oil chamber pressure p.sub.OR is recorded by the pressure sensor 25. The measured pressure values for p.sub.SGR and p.sub.OR are transmitted to the control unit 60, which uses them to determine the differential pressure (not shown in FIG. 1).

[0090] According to a further aspect of the invention, the oil-contaminated leakage or sealing gas flow does not pass unpurified from the oil chambers 19a, 19b via the air outlet 37 into the environment 9 or even into the intake area of the air inlet 70 of the compressor 1, but is fed through a gas outlet 26 via a gas discharge line 20 to an oil separator 30. The gas outlet 26 is designed as a through-opening in the compressor housing 4. The oil separator 30 can comprise several, preferably three, separation stages. In the oil separator 30, the oil (oil droplets and oil aerosols) is separated from the air. In this embodiment, the oil separator 30 comprises a fine separator 32, namely a dense coalescence filter. The separated oil collects on the dry side of the filter element.

[0091] In the embodiment shown, the oil is returned via gravity and a height difference H of the oil return line 34 that is sufficient for all operating conditions, including the pressure conditions in load operation. The oil return line 34 guides the separated oil into the oil sump 24 to a level below the oil level 23, which prevents oil mist from the gas discharge line 20 from flowing via the oil return line 34, bypassing the oil separator 30. An oil pump 36 (see FIGS. 4 and 5) can be used instead of or in addition to a height difference. The height difference H or the delivery rate of the oil pump 36 is selected according to the maximum differential pressure of the oil separator 30, in particular the coalescence filter element of the fine separator 32, which can be 100 to 300 mbar, for example.

[0092] The oil chamber pressure p.sub.OR built up by the inflow of sealing air and leakage air into the oil chamber 19a, 19b exceeds the ambient pressure p.sub.0 of the compressor housing by a sufficiently large oil separation pressure difference ?p, which is required so that the air flow flowing out of the gas outlet 26 overcomes the pressure difference of the oil separator 30. If the gas flow overcomes a pressure drop from the oil chamber 19a, 19b via the inflow side to the outflow side of the oil separator 30 of e.g. 200 mbar, for example as a pressure difference via a coalescence filter element of the fine separator 32, this corresponds to an oil separation pressure difference ?p of 20% at atmospheric pressure as the ambient pressure p.sub.0 of 1 bar on the outflow side of the oil separator 30, by which the oil chamber pressure p.sub.OR exceeds the ambient pressure p.sub.0 at least.

[0093] FIG. 2 shows a detailed illustration of a compressor 1, from which the structure of a compressor stage of a screw compressor can be seen. In this perspective, two compressor rotors 7, 8 can be seen, which are helically intermeshed and jointly compress a process gas (air). The compressor rotor 8 is driven by the compressor rotor 7 via the synchronous gear 84.

[0094] Between the inner seals 12a, 12b and outer seals 17a, 17b, two sealing gas chambers 13a, 13c and 13b, 13d are shown, which are separated from each other by additional middle seals 15a, 15b. The seals 12a, 12b, 15a, 15b, 17a, 17b are non-contacting shaft seals, as the circumferential speed and temperature are too high for contacting seals in the long term. The seals 12a, 12b, 15a, 15b, 17a, 17b can have a conveying effect. For this purpose, for example, a thread can be present, which additionally promotes leakage in the direction of the oil chambers 19a, 19b during operation.

[0095] Oil reaches the oil-lubricated bearings 18a, 18b as lubricant via the lubricating oil inlet 82. The oil chambers 19a, 19b are connected to each other via the connection line 21. The oil chamber 19b has a gas outlet 26 for connecting the common gas discharge line 20 for feeding the gas flow with the oil mist to an oil separator 30 (not shown in FIG. 2).

[0096] On the suction side 85 of the compressor rotors 7 and 8, the sealing gas chambers 13a, 13c of the two shaft seal arrangements 10a, 10b have separate sealing gas supply ducts 41, so that there are a total of four sealing gas supply ducts 41 on this side. On the pressure side 86, the sealing gas chambers 13b, 13d of the two compressor rotors 7 and 8 are connected to one another via through-holes within the compressor housing 4 via a sealing gas connection line 42, so that there are a total of two sealing gas supply ducts 41 on the pressure side 86.

[0097] Each of the compressors 1 in FIGS. 1, 3, 4 and 5 can be designed with suction-side and pressure-side shaft seal arrangements 10a, 10b, each with two sealing gas chambers 13a, 13c or 13b, 13d as shown in FIG. 2. In other figures, the perspective is chosen so that only one compressor rotor is visible for better clarity. In addition to an oil-free screw compressor, the compressor 1 could also be an oil-free compressing screw blower, roots blower or a speed compressor.

[0098] FIG. 3 shows a similar compressor 1 to that shown in FIG. 1, with the differences being explained below: The compressor 1 has a sealing gas buffer volume 48, which can be designed as a gas pressure vessel or as a cavity integrated into the compressor housing 4.

[0099] The sealing gas chambers are connected to one another by a sealing gas connection line 42, which leads through the sealing gas buffer volume 48 with an expanded flow cross-section. The sealing gas buffer volume 48 can be used to compensate for pressure fluctuations during operation of compressor 1 and to readjust the sealing chamber pressure p.sub.SGR. At the same time, this sealing gas buffer volume 48 fulfills a cooling function for the sealing gas by increasing the surface area. The sealing gas buffer volume 48 is designed in such a way that it has a separating effect and separates and collects liquid or solid contaminants before the sealing gas is fed to other sealing gas chambers. Separation can be achieved by deflectors for the sealing gas, a reduced flow velocity within the buffer volume and/or by a (coarse) demister mesh.

[0100] Furthermore, a sealing gas feed 58 is shown as an external sealing gas source, which serves to provide sealing gas in addition to the internal sealing gas source from the compressed air outlet 76 via the sealing gas supply valve 51a. A certain volume of sealing gas is stored in the sealing gas buffer volume 55, e.g. a buffer tank, in order to be able to provide a sufficient supply of sealing gas via the adjustable sealing gas supply valve 51 during transient operating states of the compressor 1, e.g. for safe start-up without pressure at the compressed air outlet 76 or safe venting (shutdown) in the event of a power failure. The non-return valves 59 prevent gas from overflowing from one sealing gas source to the other sealing gas source. The individual sealing gas sources can be used either individually or together via the sealing gas supply valves 51, 51a and 51b, depending on the detected sealing gas chamber pressure p.sub.SGR or other operating parameters. If required, sealing gas can be supplied in this way via the sealing gas supply valve 51 to the sealing gas buffer volume 48 and further to the sealing gas chambers 13a, 13b. A sealing gas feed 58, in particular an external one, and sealing gas buffer volumes 48, 55 can be used independently of one another.

[0101] The pressure p.sub.SLR in the sealing gas buffer volume 48, in the sealing gas connection line(s) 42 and in the sealing gas chambers 13 is recorded via the pressure sensor 45. The oil chamber pressure p.sub.OR in the oil chambers 19a, 19b connected via the connection line 21, the gas discharge line 20 and optionally in the oil sump 24 (not shown in FIG. 3) is recorded via the pressure sensor 25. The pressure in the sealing gas buffer volume 55 is detected by the pressure sensor 54. The pressure sensors 25, 45, 54 and the sealing gas supply valves 51, 51a, 51b are connected to a control unit 60 (not shown).

[0102] During operation, the oil is collected in the lower area of the oil separator 30. When the compressor is at a standstill and the pressures between oil separator 30 and oil chamber 19a, 19b are balanced, the oil is returned to the oil chambers 19a, 19b via the oil return line 34 using gravity and a sufficient height difference H2. Since in the present exemplary embodiment the height difference H2 alone is not sufficient to reliably prevent an oil backflow for the pressure conditions occurring during load operation, a non-return valve 39 is provided in the oil return line 34, which reliably prevents bypassing of the filter element of the oil separator 30. Return therefore only takes place when the pressure level is lowered, for example when the compressor 1 is at a standstill or possibly idling. In the embodiment shown in FIG. 1 with a sufficiently large height difference H, however, oil recirculation also takes place during load operation.

[0103] FIG. 4 shows a two-stage compressor, wherein the first compressor stage 2 and the second compressor stage 3 are connected in series in order to achieve higher final pressures. Here, the sealing gas chambers of the second compression stage 3 are connected to the sealing gas chambers of the first compression stage 2. In this way, leaks in the inner seals 12a, 12b of the second compressor stage 3 can be used to pressurize the sealing gas chambers 13a, 13b of the first compressor stage 2.

[0104] An inlet valve 71 is also shown. This can be used to reduce the pressure at the inlet of the first compressor stage 2 and at the same time to blow off the air when the compressor is idling via the relief valve 72. The non-return valve 73 prevents backflow from the compressed air outlet 76. Idle running is partly necessary to enable easier start-up of the compressor and to limit the number of motor starts when the air requirement is low. FIG. 5 also shows an air pressure sensor 77 for the final system pressure (i.e. at the interface to the compressed air network) and an air pressure sensor 78 for the final compression pressure.

[0105] A closed inlet valve 71 and open relief valve 72 (idle blow-off valve) result in a negative pressure being present in the compressor chamber of the first compressor stage 2 and also on the suction side 85 of the second compressor stage 3 during idling. As a result, some sealing gas is drawn in from the sealing gas chambers 13a, 13b via the inner seals 12a, 12b, which is in any case more advantageous than drawing in any contaminated (usually unfiltered) air from the environment or oil leaks in compressors without sealing gas. Downstream of compressor stages 2 and 3, the compressed air is cooled in a heat exchanger 74 and the condensate produced is separated and discharged via a condensate separator 75. In this way, preferably cooled air with a lower water content can be used to pressurize the sealing gas chambers 13a, 13b via the sealing gas supply valve 51.

[0106] The sealing gas chambers 13a, 13b are equipped with a negative pressure safety device 46, so that in the event of a vacuum, ambient air can enter the sealing gas chambers 13a, 13b and a negative pressure in the sealing gas chambers 13a, 13b is prevented. The negative pressure safety device 46 is designed as a non-return valve that opens towards the sealing gas chamber 13a, 13b.

[0107] The suction-side oil chambers 19a of the two compressor stages 2 and 3 are connected to each other via a common gear housing 89. The gear housing 89 accommodates the drive gear 83, which is also oil-lubricated and driven by the drive shaft 90 and which comprises the drive gearwheels connected to the suction-side shaft sections 11a for driving the compressor rotors 6. The pressure-side oil chambers 19b, in which the synchronizing gears 84 are arranged, are also connected to the common oil chamber 19a via connection line 21, in which the oil chamber pressure p.sub.OR prevails. Circulating oil lubrication with the oil sump 24, the lubricating oil pump 81 and the lubricating oil lines 80 to the bearings 18a, 18b and drive gears 83, 84 is also shown. Due to the lower speed, a contacting drive shaft seal 87 can also be used to seal the drive shaft 90 so that no or fewer leaks occur. These leaks can also be specifically drained into a leakage collection device 88 or, optionally, returned to the oil sump 24, wherein the increased oil chamber pressure p.sub.OR in the oil sump 24 or oil chamber 19a must be taken into account.

[0108] FIG. 4 shows a three-stage oil mist separation process. The large oil droplets are pre-separated in a pre-separator 31, e.g. by wire mesh/demister, wherein the separated oil can flow back into the oil chamber by gravity. The oil mist then flows through the fine separator 32, which can be a coalescence filter 32. In this case, the differential pressure across the separator element is so high that the separated oil can no longer return to the oil chamber by gravity with an acceptable height difference during operation. For this purpose, an oil return device in the form of the oil pump 36 and a backflow preventer 38 is provided in the oil return line 34 in order to be able to return the oil to the oil chamber 19a even when the compressor 1 is in continuous operation. The oil pump 36 can be designed as a peristaltic pump or vibrating diaphragm pump. The oil pump 36 can be switched on and monitored as required via the fill level sensor 35. By monitoring the filling time and pump-down time, the oil mist separation and oil return can also be monitored for correct functioning. A residual oil separator 33, designed as an adsorption filter 33, e.g. an activated carbon filter, is used as the third cleaning stage. This also adsorbs the remaining residual oil and oil vapor so that clean air is blown out into the environment 9 via the air outlet 37. In the case of process gas compression, the purified gas that escapes can also be fed directly back into the intake of compressor 1.

[0109] In exceptional cases, such as emergency venting of the oil chamber 19a, 19b, the oil mist can also be blown out of the oil chamber 19a, 19b via a blow-off valve 47, for example in the event of overpressure in the oil chamber 19a, 19b or in the event of an operating fault (power failure). To prevent too much oil from escaping into the environment 9, the oil mist is pre-cleaned via the pre-separator 31 with a low pressure loss.

[0110] FIG. 5 shows a two-stage oil-free compressing compressor 1. Here, the sealing gas chambers are subjected to different sealing gas chamber pressures p.sub.SGR, namely p.sub.SGR1 and p.sub.SGR2. The pressure levels of the sealing gas chambers 13a, 13b can be adjusted via pressure control valves 52, 53. The pressure control valve 52 is a pressure reducing valve. Two (or more) different pressure levels can be used to optimize the sealing gas flows for the respective operating state. The sealing gas chamber pressures p.sub.SGR1 and p.sub.SGR2 recorded by the individual pressure sensors 45a and 45b are measured in the sealing gas buffer volumes 43 and 44 respectively.

[0111] If a liquid should fail in the sealing gas chambers, this can be detected by the level sensor 57 and the condensate can be drained off through the drain valve 56.

[0112] Some procedural aspects of the invention, in particular with regard to the control system, are described below.

[0113] The pressure sensors 25, 45a, 45b, the regulatable sealing air supply valve 51, the blow-off valve 47 and the oil pump 36 are connected to the control unit 60, in addition to other sensors such as the air pressure sensors 77, 78 and the fill level sensor 35 as well as the liquid sensor 57, wherein further inputs for recording measurement data from other sensors and outputs for controlling other components, in particular valves, can be provided. The control unit 60 is designed in particular to monitor the oil chamber pressure p.sub.OR detected by the sensor 25 and to calculate a differential pressure to the oil chamber pressure p.sub.OR based on the sealing gas chamber pressures p.sub.SGR or p.sub.SGR1 and p.sub.SGR2 detected by the sensors 45 or 45a and 45b. Based on this differential pressure (p.sub.SGR?p.sub.OR), the control unit 60 controls the sealing gas supply valve 51 or the sealing gas supply valves 51a, 51b. The control unit 60 can be arranged (locally) on the compressor 1 or connected to the compressor 1 via a (wireless) network connection for its control and regulation. The sealing gas chamber pressure p.sub.SGR can be monitored within fixed or dynamic limit values. The control unit 60 can take into account further operating parameters of the compressor, e.g. intake and discharge pressures, speeds or temperatures of the compressor stages, in order to set the sealing gas chamber pressure or pressures for the respective operating state.

[0114] The sealing gas supply valve 51 is closed during longer downtimes to prevent unnecessary loss of compressed air.

[0115] Shortly before or when the drive of compressor 1 is started, the sealing gas supply valve 51 is already opened in order to pressurize the sealing gas chambers 13a, 13b with sufficient overpressure.

[0116] During operation, the sealing gas chamber pressure p.sub.SGR is regulated so that p.sub.SGR in the sealing gas chamber 13a, 13b is always higher than the oil chamber pressure p.sub.OR in the oil chamber 19a, 19b.

[0117] During shutdown, the pressure p.sub.SGR in the sealing gas chamber 13a, 13b is slowly reduced by feeding only a small amount of sealing gas via the sealing gas supply line 50 as required. This achieves a uniform pressure reduction both in the sealing gas buffer volumes 43, 44 with the sealing gas chambers 13a, 13b, but also in the transmission housing 89 with the oil chambers 19a, 19b. This ensures that the pressure gradient continues to run from the sealing gas chambers 13a, 13b to the oil chambers 19a, 19b and not vice versa. A sealing gas flow continues to flow into the oil chamber 19a, 19b.

LIST OF REFERENCE SIGNS

[0118] 1 Compressor [0119] 2 First compressor stage [0120] 3 Second compressor stage [0121] 4 Compressor housing [0122] 5 Compression chamber [0123] 6 Compressor rotor [0124] 7 First compressor rotor [0125] 8 Second compressor rotor [0126] 9 Environment [0127] 10a, 10b Shaft seal arrangement [0128] 11a, 11b Shaft section [0129] 12a, 12b Inner seal [0130] 13a, 13b Outer sealing gas chamber [0131] 13c, 13d Inner sealing gas chamber [0132] 14a, 14b Sealing gap [0133] 15a, 15b Middle seal [0134] 16 Rotor bearing [0135] 17a, 17b Outer seal [0136] 18a, 18b Bearing [0137] 19a, 19b Oil chamber [0138] 20 Gas discharge line [0139] 21 Connection line [0140] 23 Oil level [0141] 24 Oil sump [0142] 25 Pressure sensor (oil chamber pressure p.sub.OR) [0143] 26 Gas outlet [0144] 30 Oil separator [0145] 31 Pre-separator [0146] 32 Fine separator [0147] 33 Residual oil separator [0148] 34 Oil return line [0149] 35 Fill level sensor [0150] 36 Oil pump [0151] 37 Air outlet [0152] 38 Backflow preventer [0153] 39 Non-return valve [0154] 41 Sealing gas supply duct [0155] 42 Sealing gas connection line [0156] 43, 44 Sealing gas buffer volume [0157] 45 Pressure sensor (sealing gas chamber pressure p.sub.SGR) [0158] 45a, 45b Pressure sensor (sealing gas chamber pressure p.sub.SGR) [0159] 46 Negative pressure safety device [0160] 47 Blow-off valve [0161] 48 Sealing gas buffer volume [0162] 50 Sealing gas supply line [0163] 51 Sealing gas supply valve [0164] 51a Sealing gas supply valve [0165] 51b Sealing gas supply valve [0166] 52 Pressure control valve [0167] 53 Pressure control valve [0168] 54 Pressure sensor [0169] 55 Sealing gas buffer volume [0170] 56 Drain valve [0171] 57 Liquid sensor [0172] 58 Sealing gas feed [0173] 59 Non-return valve [0174] 60 Control unit [0175] 70 Air inlet [0176] 71 Inlet valve [0177] 72 Relief valve [0178] 73 Non-return valve [0179] 74 Heat exchanger (compressed air cooler) [0180] 75 Condensate separator [0181] 76 Compressed air outlet [0182] 77 Air pressure sensor for system end pressure [0183] 78 Air pressure sensor for compression end pressure [0184] 80 Lubricating oil line [0185] 81 Lubricating oil pump [0186] 82 Lubricating oil ingress [0187] 83 Drive gear [0188] 84 Synchronized gear [0189] 85 Suction side [0190] 86 Pressure side [0191] 87 Drive shaft seal [0192] 88 Leakage collection device [0193] 89 Gear housing [0194] 90 Drive shaft